STROBILI 



453 



the back or lower side of the niicrosporophylls are the micro- 

 sporangia, usually two, and each contains numerous microspores. 

 Nearly opposite each other on the microspore are two air-sacs 

 whereby the spores are easily carried by the wind. When the 

 spores are mature, the microsporangia or pollen sacs open by 

 longitudinal slits, and the pollen shatters out, often like small 



Fig. 402. The staminate structures of the Pine. A, cluster of staminate 

 strobiU ( X about f ) . B, a. staminate strobilus enlarged, showing the arrange- 

 ment of the microsporophylls. C, a microsporophyll, showing the two 

 sporangia (m) ; D, microspore showing the two wings and two cells of the male 

 gametophyte. 



clouds of dust. The wind carries the pollen about, and some 

 reaches the ovulate strobili, but much the larger part of it is 

 wasted. Sometimes pollen accumulates on walks under Pines 

 that are shedding their pollen until the walks look as if they had 

 been sprinkled with finely powdered sulphur. 



The ovulate strohili or cones appear near the tips of the new 

 growths in early spring. Usually they are smaller when they 

 first appear than the staminate cones, but they persist and, after 

 a growth of two seasons, become the conspicuous scaly cones so 

 familiar on or about pine trees. Sometimes several occur to- 



